Fiber optics enable the transmission of long strings of data in a serial fashion from a driver to a receiver at long distances (kilometers) at very high data rates (billions of bits per second). This is in contrast to traditional electrical wires which allow data to be transmitted for only short distances at these data rates (10's of meters).
High performance computers require system buses between elements of a computing system to have even higher bandwidths (100's of millions of bytes per second). The use of a single fiber optic cable running at its maximum bandwidth can be insufficient to serve as a system bus between elements of a computing system.
In the prior art, a classical solution to the problem of inadequate bandwidth on a single carrier is to transmit the bits of each data word, in parallel, one over each of a plurality of carriers (a parallel bus). Another solution, known as striping, entails sending a plurality of serial data words, in parallel, one over each of a plurality of carriers. These solutions, however, share a common problem in that skew can develop between the parallel bits or words as they are sent over the bus.
In addition to high bandwidth, high performance computers also require communication with low latency. In other words, the total time it takes to transmit a message, process the message, and return the response must be kept to a minimum. In prior art, information is transmitted in frames, and all of the information required to transmit a frame is fetched from main processor storage before frame transmission is started, thereby adding latency. Also, all subsequent frames must wait until the present frame is completed; therefore, any higher priority messages cannot be transmitted until the link is idle. A similar situation exists when receiving frames; the entire frame must be received before it is sent to the main processor storage.
The skew introduced by multiple conductors further complicates the interruption of transmission of one message to send a higher priority message. All of the conductors have to be stopped and started in a manner that allows the receiver to keep track of which frames belong to which messages.
Thus what is needed is an improved method for transmitting data words over a plurality of carriers such as multiple fiber optic filaments in a way that allows the lowest possible latency by starling frames before all of the information is fetched from main processor storage, and further by allowing the interleaving of these frames.